Segment routing (SR) is a type of underlay network that helps realize various overlay technologies. In a SR network, a node (i.e., at an ingress of the network) can steer a packet using a controlled set of instructions, called segments, by prepending a header of segments to the packet. A segment can represent any instructions, topological or service-based (e.g., instructions may include, for example, but not limited to, a destination address, a service, a context, a locator, a local value or a global value, as well as a forwarding construct such as an IGP-based or BGP-based forwarding construct). Interior gateway protocol (IGP) is a type of protocol used for exchanging routing information between gateways (e.g., routers) within an autonomous system (AS). Border Gateway Protocol (BGP) is another protocol designed to exchange routing and reachability information among autonomous systems on the Internet.
A segment may include a segment identifier; the two terms are interchangeably used herein. Multiple segments are combined to form an order list of instructions, the order list is also referred to as a stack (of segment identifiers).
In certain circumstances, it is desired to capture packets in a SR traffic flow, for example, by network administrators, for analysis—such as to identify applications operating on a given SR network; identify points of intrusions to identify security flaws and breaches; identify data leakages; troubleshoot occurrences of undesired network events; identify and/or recover lost or stolen data and packets; determine extent of network elements comprised by virus and malware; assess impact of changes within a network; and ensure long-term compliance issues.